Lamp sockets used in exterior vehicle lighting applications are typically made from plastic. One commonly used plastic alloy for these sockets is a glass filled blend of polyphenylene oxide (PPO) and nylon 6,6, sold by General Electric Company under the trademark Noryl GTX 810. This plastic, as with most others, outgases to some extent during normal use in its intended vehicle lighting application. Outgassing of plastics such as the Noryl GTX 810 is known to cause fogging on the other lamp assembly components (e.g., lenses and/or reflectors) which can adversely affect the appearance, aesthetics, and photometric performance of the overall lamp assembly. Various approaches have been proposed for reducing the outgassing of such materials. See, for example, U.S. Pat. No. 6,012,830 to Frazier which discloses a light shield for a vehicle headlamp that uses a titanium carbide coating that reportedly does not outgas over the life of the headlamp. As another example, PCT published application No. WO 02/075863 A1 to Heath discloses a lamp socket formed from polyetherimide (PEI) which has been found to reduce fogging of the lenses and reflectors when compared to the Noryl GTX 810 plastic.
In a typical vehicle exterior signal lighting application or similar application, such as in a S-8/GT-8 bulb application, this fogging shows up over time as a film that forms on the interior surface of the lens and reflector surfaces used in the lamp assembly. For sockets using the Noryl GTX 810, this film has previously been analyzed and determined to be cyclic dimers, C12H22O2N2 from the nylon 6,6 in the plastic. More recent analysis of the film from testing of the lamp sockets at 130° C. for 90 minutes has shown that the lamp socket produces styrene and toluene type structures. Furthermore, under the same testing conditions, it was found that the nylon sleeve, or base, used on the GT-8 bulb was itself producing aniline and benzene type structures.
While the use of PEI has been identified for lamp socket assemblies for exterior lighting applications, including use for the socket, housing or both, there exists a need to identify additional materials which may be used for lamp sockets and lamp assemblies of the types described above.